Elucidate the role of the host cell in determining the outcome of viral infection. The abortive infection of bacteriophage T7 in cells of Escherichia coli containing F factors or certain R factors serves as the model system. Analysis of plasmid genes required for the abortive T7 infection (pif gene) will be coupled with analysis of host functions which prevent the interference with T7 development. Host RNA polymerase, transcription termination factors, ribosomal proteins and DNA gyrase enzyme are among the functions to be examined. The major goals of the present year have been to study the organization and regulation of pif gene expression by isolating operon and protein fusions which place beta-galactosidase under the control of pif regulatory sequences. The existence of plasmids bearing portions of the pif region will now make it possible to analyze the contribution of each pif protein to the inhibition of T7 infection. Having the beta-galactosidase gene fused to pifA and pifB will allow us to quantitate the effects of host mutations which enhance and decrease pif expression. We will thus be able to demonstrate whether the control of pif function is at the level of transcription or function.